The concept originated from a late episode of The Saint titled 'The Ex-King of Diamonds', in which Simon Templar (Moore) partners with a Texas oilman played by Stuart Damon; producers Robert S. Baker and Lew Grade liked the pairing enough to fund a whole new series around it.

Before Tony Curtis was cast, the American co-star role was first offered to Rock Hudson and Glenn Ford, both of whom turned it down; ITC then asked ABC for a list of suitable American actors, which included Curtis.

At 46 years old during filming, Tony Curtis insisted on performing all of his own stunts and fight sequences.

The title sequence was deliberately designed so that neither actor would appear to have top billing, a condition both Roger Moore and Tony Curtis had stipulated before agreeing to co-star.

Roger Moore acted as his own wardrobe stylist on the show, reflecting his genuine interest in fashion and his role as director of textile firm Pearson and Foster; every episode credited 'Lord Sinclair's clothes designed by Roger Moore' in his own large signature.

Only one series was made because Roger Moore left to become James Bond; producer Robert Baker revealed that Lew Grade was willing to finance a second series by replacing Moore with Noel Harrison, son of Rex Harrison, but Baker convinced him the Moore-Curtis dynamic was irreplaceable.

Director Val Guest recalled that Tony Curtis frequently complained on set and used cannabis during filming; according to Roger Moore's autobiography, Curtis even smoked marijuana in front of a police officer while filming at 10 Downing Street.

During a tense moment on the Croisette in Cannes when Curtis was complaining about wardrobe, Roger Moore grabbed him by the lapels and quipped 'and to think those lips once kissed Piper Laurie,' which made the entire film unit burst out laughing.

Danny Wilde's red Ferrari Dino 246 GT and Brett Sinclair's Bahama Yellow Aston Martin DBS, complete with the personalized 'BS 1' number plate (an echo of Simon Templar's 'ST 1' from The Saint), were provided free by their manufacturers; the real owner of the 'BS 1' plate, Billy Smart Jr., allowed its use in the series.

The German dubbed version, Die Zwei, rewrote the dialogue so extensively with slang and fourth-wall-breaking jokes (even referencing Moore's future role as James Bond) that researchers at the University of Hamburg found the only element it shared with the original was the footage itself; the French version Amicalement Vôtre was based on this altered German dub rather than the original English scripts.

Despite disappointing performance in the US, where it aired opposite Mission: Impossible and was not scheduled in prime time, the series became a major hit across Continental Europe, winning a Logie Award in Australia, a TP de Oro in Spain, and a Bambi award for both Curtis and Moore in Germany.

A film remake was announced in 2005 with Steve Coogan and Ben Stiller, and later in 2007 with Hugh Grant and George Clooney attached, slated for a December 2008 release, but the project was never completed.

John Barry's synth-driven theme has had a lasting cultural afterlife: it was used by ska band The Specials as walk-on music, sampled by Snoop Dogg in 'Lavender' and by Tyler, the Creator in 'Rise!', and used diegetically in the film Nocturama.